1. Field of the Invention
The present invention relates to microporous crumbs of a hydrogenated block copolymer comprising at least one polymer block of a vinyl aromatic compound and at least one polymer block of a conjugated diene, and the process for producing the same. The crumbs of the present invention absorb a softening agent, a plasticizer and the like uniformly and rapidly, have an excellent handling property, even after absorption, and provide molding compounds free of non-melted residuals, i.e., residual solids remaining as not melted (hereinafter simply referred to as "non-melted matters").
2. Related Art of the Invention
The hydrogenated block copolymer comprising at least one polymer block of a vinyl aromatic compound and at least one polymer block of a conjugated diene (hereinafter simply referred to as "hydrogenated block copolymer") is not only excellent in weather proofness, heat resistance, impact resistance and flexibility but also shows, without vulcanization, good strength and elastic property comparable to that of conventional vulcanized rubber, so that it has been utilized widely in the fields of daily necessities, automobile parts, light electrical appliance parts, parts of various industrial products and the like.
As prior art references which disclose the process for production of hydrogenated block copolymers, the following documents are exemplified: Canadian Patent No. 815,575, British Patent No. 1,043,023 and U.S. Pat. Nos. 3,333,024, 3,644,588, 3,686,366 and 3,700,748.
The hydrogenated block copolymer is usually produced by polymerizing a vinyl aromatic compound and a conjugated diene in a hydrocarbon solvent to give a block copolymer and hydrogenating said block copolymer. This process requires a step of isolating the hydrogenated block copolymer from the hydrocarbon solvent, because the hydrogenated block copolymer is obtained dissolved or suspended in the solvent. Various methods have been utilized to isolate the hydrogenated block copolymer from the hydrocarbon solvent. Among them, a steam stripping method has been known as described, for example, in Japanese Patent Publication Nos. Sho 57-47684 and Sho 57-53363, wherein a solution of a hydrogenated block copolymer in the hydrocarbon solvent is introduced into hot water in order to remove the solvent by distillation together with water and to make crumbs of the hydrogenated block copolymer.
However, crumbs of the hydrogenated block copolymer obtained by the steam stripping method suffer from the following disadvantages: (a) The crumbs cannot absorb a softening agent, a plasticizer and the like uniformly and rapidly, since the total volume of the micropores of the crumbs is too small or the ratio of the sum of the volume of micropores having a pore diameter within a specific range relative to the total volume of the micropores of the crumbs is too small although the crumbs have micropores with a moderate pore diameter on average. (b) The crumbs have a poor handling property after the absorption of the softening agent, plasticizer and the like, and provide a molding compound with considerable non-melted matters when kneaded with a resin such as polypropylene or polyethylene, since the pore diameter of the crumbs is too large or the bulk density of the crumbs is too low.